Acoustics - Criteria for projecting recording studios

Generally speaking a recording studio comprises two rooms: the recording room and the control room. The following diagram illustrates a possible recording studio setup in which an extra recording room is present for the isolated recording of the drum-kit:

General room layout in a recording studio

The recording room is where the sounds are produced and recorded. The acoustics of this room is a crucial factor in getting a good recording done. A recording room that has bad acoustics jeopardizes the quality of the recording to such an extent that none of the effects at our disposal during mixing could make up for the poor sound quality. The reverb time and the quality of the reverberated sound (in principle, the reverberated sound should contain traces of all the original sound's frequencies) are very important factors. Just as important is the correct isolation of the room from external noise (referring to the previous diagram, it is of utmost importance that the drum-kit sounds remain isolated in recording room 1 and don't reach the microphones in recording room 2). Having already spoken of the rooms' acoustic criteria, let's now take a look at how the acoustic isolation of the various rooms takes place.

One of the sound transmission means we need to pay particular attention to is propagation through walls and floors. They are excellent media for the transmission of sound and can carry it from one environment to another (how often have you heard your next door neighbour banging away... as he hangs up his wife's favourite painting? :-P ). For this reason, walls, ceilings and floors get as isolated as possible. Doors and windows are also good sound transmitters and must therefore be built using the right criteria.

Floors (ceilings):
a relatively affordable solution to make a floor soundproof is to build a new layer, made up of different isolating layers, on top of the one already present. The following figure illustrates this solution:

Acoustic isolation of a floor (cheap solution)

Let's consider the room's cement floor. On top of it we spread a layer of neoprene to absorb the vibrations transmitted by the cement. On top of the neoprene we'd then add some 10 cm-tall wooden supports to sustain the new floor that is placed on top of them. Then another layer of neoprene is put on the wood to sustain the final layer which will be the actual floor of the recording room, and which can be made of wood again. This way the air in between the two floors acts as a further isolation from the sounds issuing from the cement floor.

Large recording studios resolve the problem in a rather more radical way: a whole extra cement floor is added. The technique that is employed consists in making and adding a cement floor to the already existing one. The new floor has large screws inside it, which, once the cement has dried up, are unscrewed, thus lifting the second floor off the original floor:

Acoustic isolation of a floor (expensive solution)

As far as ceilings is concerned, the new isolated ceiling is hung to the original with hooks, which isolates it acoustically. Then isolating material is wedged between the two ceilings acting as acoustic isolator.

Walls:
as already mentioned, the walls shouldn't stand parallel to each other and this is true for any large surface in the environment. Moreover, they ought to be isolated both from the ceiling and the floor as well as the original walls. Internal walls are thus constructed and fitted inserting isolating material between the two walls. Also, the walls are enclosed within two isolating layers (neoprene again, for example) which conjoin them to the ceiling and the floor. The following figure illustrates part of a room whose ceiling, floor and walls have been sound-proofed:

Section of a room that has been sound-proofed

Connections:
every room is connected to the others through a series of sockets and leads that pass from one to another. It is best to decouple the connections between rooms as much as possible, as shown in the following figure:

Electrical connections between two rooms

Doors:
when possible, double-doors should be fitted in order to interrupt the transmission of sound, and great attention should be dedicated to seal all possible crevices with gum-seal. In this case too, the guideline to avoid parallel surfaces stands.

Windows:
the only necessary window in a recording studio is the one between the recording room and the control room. It is made using two very thick glass panels, again, in order to ensure acoustic isolation. The two glass panels are also fixed non-parallel to each other to avoid resonance phenomena, as shown in the following diagram: